I got nailed on exactly the same thing.
I referred to a fellow as an "Oriental" in a workshop. He had the skin color and facial features which distinguish an "Oriental" from an "Occidental", which I am.
Got politely pummeled. I will accept that times have changed. And I still have no idea as to what is offensive about calling an Asian an Oriental. There is no offense in my mind, no prejudice, no interest except in distinguishing one person from another. And to look at some people, it is clear they are Oriental. Unmistakeable. Well, almost.